In the application of a powder to the surface of a part, the part is usually arranged on a conveyor belt which moves the part under the discharge area of the applying apparatus. A quantity of powder to be applied is stored in a hopper. A second conveyor is then utilized to transfer a measured amount of the powder from the hopper to the discharge area where it is permitted to fall to the surface of the part. There afe several known devices for accomplishing this.
One such prior art device includes a rotating cylinder, or drum, having an outer surface which engages an opening in the bottom of a hopper. The outer surface effectively blocks the opening thereby serving as a bottom to the hopper. A space is provided between one edge of the hopper wall adjacent the opening and the surface of the rotating drum. As the drum rotates, powder in the bottom of the hopper is carried along with the surface of the drum, under the spaced edge. As the drum continues to turn, the powder eventually falls off the drum to a part below. For a more complete description of this type of structure see U.S. Pat. No. 3,534,787 which issued Oct. 20, 1970 to Heck.
A second such prior art device utilizes a somewhat horizontally disposed conveyor belt to pick up powder contained in the bottom of the hopper in a manner similar to that of the drum described above. A space is provided between an edge of the hopper and the conveyor belt so that particles of powder may be picked up from the hopper and carried along the surface of the belt. The belt is a continuous web carried by a pair of rollers at opposite ends, one being a drive roller and the other an idler roller. As the powder particles reach the end of the conveyor belt they fall onto the surface of a part which is arranged on another conveyor belt vertically below. For a more complete description of this type of structure see U.S. Pat. No. 2,943,599 which issued July 5, 1960 to Heck.
A third such prior art device utilizes a combination of several conveyor belts, mechanical agitators, and blowers to move powder particles from a hopper to the surface of a moving belt. An example of this type of apparatus is disclosed in U.S. Pat. No. 3,978,250 which issued Aug. 31, 1976 to Griten.
All of these prior art devices apply the powder in a continuous, uninterruped stream having a constant width. This results in the undesirable and wasteful application of powder to the conveyor belt that is transporting the parts. Where the parts are rectangular in shape this waste can be reduced by limiting the width of the discharge area to that of the surface to be coated and closely spacing the parts on the conveyor. Where the parts are other than rectangular in shape there is necessarily a greater area of exposed conveyor belt resulting in additional waste. What is desired is to apply the powder evenly to the surface of a part while substantially reducing the amount of powder applied to areas adjacent the part. The present invention achieves this by the novel use of a moving, variable width aperture structure described herein.